Flex in a Transformer

[Ernest Bonham]

Can anyone tell me if or where in the NEC it is required to flex in a transfomer. I know I do it all the time for it makes for a easy clean install and also keeps the sound level from the transformer being transmitted thru the pathway. If I'm correct the NEC does not require this but most local code do.

Any help would be thankfull.

 

[charlie b]

If I'm correct the NEC does not require this but most local code do.

The NEC does not require this, but I cannot say anything about "most" local codes. Actually, I would be surprised if anyone made this a requirement.

Welcome to the forum.

 

[electricalperson]

its not a code requirement it might be a spec that an engineer might ask for but i never seen it in the code book or even had an inspector ask for it. you use greenfield or other flexible connections if noise is a problem. i always use it sometimes it makes life easier

 

[izak]

sometimes i wish the shop i work for would get away from flexing transformers...

at least in certain situations.

it can be: UGLY

More Expensive (fittings)

More time consuming to install (trying to get 4-500s thru flex 90s)

 

[infinity]

More time consuming to install (trying to get 4-500s thru flex 90s)

You're right. Had to install 5-600's in a 3' piece of 4" FMC with two 90 degree angle connectors, one on each end. The transformer is mounted on springs. The spec called for a lateral movement of top of the transformer of 3/4 of an inch in either direction. Who designs this stuff?

 

[jrannis]

Of course its best to stub up under them if you can.
I havent seen a transformer yet that wasnt installed on isolator pads inside of the enclosure. I wouldnt wire them in flex unless it was a spec.

I took over a job where the last PM misread the spec and ordered Liquidtite and all the fittings for interior utilization transformer connections.
Expensive mistake!

 

[izak]

mistake? I worked for a shop that uses EXCLUSIVELY Seal-Tite for flexing transformers! With bond Bushings!

The guys who have done thier whole apprenticeship there think its CODE to do it that way.

 

[hillbilly1]

I have not found it in the code either yet, but the AHJ can reference the standard for "Good Workmanship in Electrical Construction" NECA 1-2006, which does require "Raceway(s) to equipment subject to vibration shall be terminated in a box and final connections made with flexible conduit." Stubbing up under the transformer is allowed with the limitation of a rise no more than 3 inches above the bottom of an enclosure. (NEC 408.5)

 

[iwire]

I have not found it in the code either yet, but the AHJ can reference the standard for "Good Workmanship in Electrical Construction" NECA 1-2006, which does require "Raceway(s) to equipment subject to vibration shall be terminated in a box and final connections made with flexible conduit."

IMO that is long stretch and an EC that had mind to could fight it.

The NFPA style manual list both neat and workmanlike as vague and unenforceable.

 

[jrannis]

I have not found it in the code either yet, but the AHJ can reference the standard for "Good Workmanship in Electrical Construction" NECA 1-2006, which does require "Raceway(s) to equipment subject to vibration shall be terminated in a box and final connections made with flexible conduit." Stubbing up under the transformer is allowed with the limitation of a rise no more than 3 inches above the bottom of an enclosure. (NEC 408.5)

The transformer itself might vibrate but I usually anchor the transformer enclosure to the floor. It doesnt vibrate or move much after that:smile:

 

[celtic]

Stubbing up under the transformer is allowed with the limitation of a rise no more than 3 inches above the bottom of an enclosure. (NEC 408.5)

408.5 Clearance for Conductor Entering Bus Enclosures.
Where conduits or other raceways enter a switchboard, floor-standing panelboard, or similar enclosure...

Is a transformer a "similar enclosure"?
I think not.

The closest you will find in 450 (transformers) is 450.12 which directs the user to the 3xx's for wire bending and such.

 

[hillbilly1]

According to NECA 1-2006 it is, just quoting them. I myself don't like the looks of it, but have seen it done often.

 

[William1978]

..............

 

[William1978]

 

[William1978]

I give up I was trying to post an picture.

 

[terille]

Transformer flex

Transformer flex

You need flex due to vibration of the transformer

 

[iwire]

You need flex due to vibration of the transformer

Did you even read the thread before posting. :grin:

As an instruter I hope you know the NEC does not require flex and many transformer are bolted solidly to a cement floor.

Flex is just a design decision, flex, wireway, EMT, MC are all ways you could connect a transformer.

 

[William1978]

You need flex due to vibration of the transformer

All the x-fmers that I ever installed that were on the 1st floor of a building I would rough in the slab with pvc and stub up just in front xo with the primary,secondary and the ground. Pvc is a whole lot cheaper than flex and conn.

 

[celtic]

All the x-fmers that I ever installed that were on the 1st floor of a building ....

What did you do on the upper floors?:wink:

 

[jrannis]

You need flex due to vibration of the transformer

Maybe you need, but I dont need